The simplest switching network capable of interconnecting N.sub.1 input ports and N.sub.2 output ports is a rectangular N.sub.1 .times.N.sub.2 matrix of switching elements or crosspoints. Such a matrix is strictly non-blocking in that any idle output port can selectively connect any input port regardless of the state of interconnection among other input and output ports.
Switching networks useful in broadcast service require a large number of output ports that selectively can be connected to any one of a large number of input ports. The audio and video signals switched in the networks have a very wide bandwidth and dynamic range at power levels requiring expensive switches or crosspoints. Accordingly, minimizing the total number of crosspoints required becomes important simply from a cost standpoint.
Reduction in the total number of required crosspoints from N.sub.1 .times.N.sub.2 can be achieved by multiple stage switching as is described by Charles Clos in his article "A Study of Non-Blocking Switching Networks" published in The Bell System Technical Journal, March 1953, pages 406-424. Three-stage multiconnection Clos networks have been designed which are non-blocking in the wide sense, i.e., non-blocking when a particular connection strategy is followed, as discussed in the article by F.K. Hwang "Three-Stage Multiconnection Networks which are Non-Blocking in the Wide Sense" published in The Bell System Technical Journal, Vol. 58, No. 10, December 1979, pages 2183-2187.
Rearrangeable multi-stage switching networks for broadcast service are described by Gaylord W. Richards and Frank K. Hwang in "A Two-Stage Rearrangeable Broadcast Switching Network" published in the IEEE Transactions on Communications, Vol. Com33, No. 10, October 1985; in Richards U.S. Pat. No. 4,566,007 entitled "Rearrangeable Multiconnection Switching Networks" and in the references there cited; in G. W. Richards U.S. Pat. No. 4,817,083 entitled "Rearrangeable Multiconnection Switching Networks Employing Both Space Division and Time Division Switching" and in other publications there identified.
In the foregoing prior art, a recognized problem exists in the expense and reduced communication integrity of known multiconnection broadcast quality switching networks.